Researchers from MIT have created a water filter fashioned from a
small piece of sapwood, an inexpensive and disposable technology
that could help millions of people in the developing world who don't
have access to safe drinking water.

The key ingredient is plant xylem — a tissue in plants made up of
vessels and tiny pores. The vessel pathways allow sap to travel
up from the tree's roots to the shoots, while the pores trap air
bubbles so they don't spread into the wood and kill the tree.

“It’s the same problem with water filtration where we want to
filter out microbes but maintain a high flow rate," Rohit Karnik,
co-author of the study and an associate professor of mechanical
engineering at MIT, said in a media release.

It's also a coincidence that the size of these xylem pores,
anywhere from a few nanometers to 500 nanometers depending on the
plant, are the perfect size for blocking out pathogens,
researchers said in a study published Wednesday in the journal PLoS One.

For this study, researchers used plant xylem from the branch of
white pine trees. The device was made by simply peeling the bark
from the branch, cutting it up into inch-long pieces, and shoving
it into a plastic tube. They used a simple tube fastener to
provide a tight seal.

Voila!

Researchers design a
simple filter by peeling the bark off a small section of white
pine, then inserting and securing it within plastic
tubing.MIT

In the lab, the MIT team found that the tree branch filtered out
99% of E. coli bacteria from water. In an interview with Popular Mechanics, Rick
Andrews, global business development director of water systems at
the National Sanitation Foundation International, cautioned that
the results might be slightly different if conducted in a
real-world setting. It's possible that very polluted water could
clog the pores of the tree branch making it less effective.

But the design is still a positive step forward. Because xylem
filters are low-tech and made from wood, an easily available
material, they could be produced on a small-scale at a much lower
cost than current water-disinfecting technologies, such as
boiling (which requires lots of fuel), expensive chlorine
treatments, and UV lamps, according to the study.

The xylem filters aren't only applicable in the developing world.
Researchers think that sapwood could also be used as a makeshift
filter on a camping trip.

"Break off a branch from the nearest pine tree, peel away the
bark, and slowly pour lake water through the stick," they said.

The MIT team is now looking at the xylem tissue of other plants,
particularly from locally available sources, to see how well they
filter out bacteria and other pathogens.